The novel hybrid metal-graphene metasurfaces for broadband focusing and beam-steering in farfield at the terahertz frequencies

Abstract

A hybrid metal-graphene metasurface was proposed and researched in terahertz (THz) frequencies. It is found that these hybrid structure metasurfaces give rise to a larger phase variation in comparison to bare graphene metasurface. Based on the analysis of electric field of the hybrid structures, it implies that due to the enhanced localized electric field and the Fabry-Perot resonance cause the phase increasing quadratically with the improvement of the graphene Fermi energy (EF) in hybrid metal-graphene structures. By designing different metal sizes and modulating EF, the structure shows up to 295° of smooth phase modulation at the frequency of 4.5 THz. Based on the phase profile design, a reflection-type focusing metasurface with near 1000 μm focal length in a broadband frequency range from 4 to 4.8 THz and 1-bit dynamically tunable coding metasurface to steer the reflected THz waves into multiple beams in farfield were both demonstrated successively. Moreover, the degree of freedom for beam-steering of 2-bit coding metasurfaces was enhanced and the process of manipulation was also qualitatively interpreted by the convolution principle. This work may supply a potentially effective method to instruct the design of desirable metasurfaces with multi-function in the modulation of electromagnetic waves.